Objectivity is a central philosophical concept, related to reality and truth, which has been variously defined by sources. Generally, objectivity means the state or quality of being true even outside of a subject's individual biases, interpretations, feelings, and imaginings. A proposition is generally considered objectively true (to have objective truth) when its truth conditions are met without biases caused by feelings, ideas, opinions, etc., of a sentient subject. A second, broader meaning of the term refers to the ability in any context to judge fairly, without partiality or external influence. This second meaning of objectivity is sometimes used synonymously with neutrality.

Stronger versions of this claim hold that there is only one correct description of this reality. If it is true that reality is mind-independent, then reality might include objects that are unknown to consciousness and thus might include objects not the subject of intensionality. Objectivity in referring requires a definition of truth. According to metaphysical objectivists, an object may truthfully be said to have this or that attribute, as in the statement "This object exists," whereas the statement "This object is true" or "false" is meaningless. For them, only propositions have truth values. The terms "objectivity" and "objectivism" are not synonymous, with objectivism being an ontological theory that incorporates a commitment to the objectivity of objects.

Plato's idealism was a form of metaphysical objectivism, holding that the Ideas exist objectively and independently. Berkeley'sempiricistidealism, on the other hand, could be called a subjectivism: he held that things only exist to the extent that they are perceived. Both theories claim methods of objectivity. Plato's definition of objectivity can be found in his epistemology, which takes as a model mathematics, and his metaphysics, where knowledge of the ontological status of objects and ideas is resistant to change.

Plato considered knowledge of geometry a condition of philosophical knowledge, both being concerned with universal truths. Plato's opposition between objective knowledge and doxa (opinions) became the basis for later philosophies intent on resolving the problem of reality, knowledge, and human existence. Personal opinions belong to the changing sphere of the sensible, opposed to a fixed and eternal incorporeal realm that is mutually intelligible.

Where Plato distinguishes between what and how we know things (epistemology), and their ontological status as things (metaphysics), subjectivism such as Berkeley's and a mind dependence of knowledge and reality fails to distinguish between what one knows and what is to be known, or at least explains the distinction superficially. In Platonic terms, a criticism of subjectivism is that it is difficult to distinguish between knowledge, doxa, and subjective knowledge (true belief), distinctions that Plato makes.

The importance of perception in evaluating and understanding objective reality is debated. Realists argue that perception is key in directly observing objective reality, while instrumentalists hold that perception is not necessarily useful in directly observing objective reality, but is useful in interpreting and predicting reality. The concepts that encompasses these ideas are important in the philosophy of science.

The term, "ethical subjectivism," covers two distinct theories in ethics. According to cognitive versions of ethical subjectivism, the truth of moral statements depends upon people's values, attitudes, feelings, or beliefs. Some forms of cognitivist ethical subjectivism can be counted as forms of realism, others are forms of anti-realism. David Hume is a foundational figure for cognitive ethical subjectivism. On a standard interpretation of his theory, a trait of character counts as a moral virtue when it evokes a sentiment of approbation in a sympathetic, informed, and rational human observer. Similarly, Roderick Firth's ideal observer theory held that right acts are those that an impartial, rational observer would approve of. William James, another ethical subjectivist, held that an end is good (to or for a person) just in the case it is desired by that person (see also ethical egoism). According to non-cognitive versions of ethical subjectivism, such as emotivism, prescriptivism, and expressivism, ethical statements cannot be true or false, at all: rather, they are expressions of personal feelings or commands. For example, on A. J. Ayer's emotivism, the statement, "Murder is wrong" is equivalent in meaning to the emotive, "Murder, Boo!"

According to the ethical objectivist, the truth or falsehood of typical moral judgments does not depend upon the beliefs or feelings of any person or group of persons. This view holds that moral propositions are analogous to propositions about chemistry, biology, or history, in so much as they are true despite what anyone believes, hopes, wishes, or feelings. When they fail to describe this mind-independent moral reality, they are false—no matter what anyone believes, hopes, wishes, or feels.

There are many versions of ethical objectivism, including various religious views of morality, Platonistic intuitionism, Kantianism, utilitarianism, and certain forms of ethical egoism and contractualism. Note that Platonists define ethical objectivism in an even more narrow way, so that it requires the existence of intrinsic value. Consequently, they reject the idea that contractualists or egoists could be ethical objectivists. Objectivism, in turn, places primacy on the origin of the frame of reference—and, as such, considers any arbitrary frame of reference ultimately a form of ethical subjectivism by a transitive property, even when the frame incidentally coincides with reality and can be used for measurements.